The invention relates to a heterostructure semiconductor laser diode with a layer sequence formed on a substrate, wherein a laser-active layer is arranged between enclosing layers of respectively opposite conductivity types, wherein an additional layer and a cover layer of the same conductivity type as the substrate are formed on the side of the layer sequence facing away from the substrate, and wherein the cover layer includes an oppositely doped semiconductor area which penetrates the additional layer in a strip-shaped zone extending perpendicularly to the exit surface of the laser radiation in the area of the plane of symmetry below a v-groove-shaped recess and extends into the layer located thereunder, whereby the current flowing in the forward direction of the semiconductor laser diode is confined to a narrow, strip-shaped area of the laser-active layer.
A heterostructure semiconductor laser diode with a v-groove-shaped recess is known from German Pat. No. 2,822,146. A solution is proposed therein for improved adaptation of a semiconductor laser to, for example, an optical fiber provided for light conduction, in particular, a single-mode optical fiber where there is an essentially linear connection between light characteristic and current characteristic.
In these conventional semiconductor lasers, the active area or strip is pumped up to the resonator mirrors. The light in the laser-active layer exhibiting a constant band gap is, furthermore, conducted as far as the mirrors. Heat is generated at the mirrors by surface recombination, and the overpopulation in the valence or conduction band is simultaneously reduced. As a result, the directly generated heat together with the absorption induced by the absence of overpopulation cause a gradual degradation of the mirrors with relatively low output power and a strong degradation with high output power.